Process and apparatus for producing finned tubing



,1968 A. Y. GUNTER ETAL 3,417,451

PROCESS AND APPARATUS FOR PRODUCING FINNED TUBING Original Filed Feb. 24. 1964 4 Sheets-Sheet l HHHIHHHHHHIIUH ADDISON Y GUNTER THOMAS E O INVENTORS A TTORNE YS Dec. 24, 1968 A. Y. GUNTER ET AL 3,417,451

ADD/501v Y GUNTER J' THOMAS E. OWE/v INVENTORS BY M, #7 llwa' ATTORNEYS Dec. 24, 1968 GUNTER ET AL 3,417,451

PROCESS AND APPARATUS FOR PRODUCING FINNED TUBING Griginal Filed Feb. 24, 1964 4 Sheets-Sheet 3 ,6 a I I I/ I9 I L I 20 .L -3 16b 5 I! I 40 39 l 7 117.5 /l5c ADD/SON Y GUNTERf' THOMAS E OWEN INVENTORS ATTORNEYS Dec. 24, 1968 T R ET AL 3,417,451

PROCESS AND APPARATUS FOR PRODUCING FINNED TUBING Original Filed Feb. 24. 1964 4 Sheets-Sheet 4 ADDISON Y GUNTER s THOMAS E. OWEN INVENTORS BYM, W H74 1 M ATTORNEYS United States Fatent @fice 3,417,451 Patented Dec. 24, 1968 Feb. 24, 1964. This application July 6, 1966, Ser. N0. 565,044

12 Claims. (Cl. 29157.3)

This application is a continuation of our copending application, Ser. No. 346,833, filed Feb. 24, 1964, now abandoned, and entitled Process and Apparatus for Producing Finned Tubing.

This invention relates to the art of producing finned tubing of the type used for heat transfer purposes; and particularly relates to improved apparatus and methods for manufacturing helically wound finned tubing.

In the manufacture of finned tubing of this type, it has been customary to wind a thin strip of metal edgewise about a tube as the tube is simultaneously advanced and rotated. For this purpose, and prior to being wound about the tube, the thin strip of metal is passed between variously designed forming rolls to differentially thin it in increasing amounts from its inner to its outer edge. Thus, the strip is formed into a helical fin as it leaves the forming rolls and its inner edge is wrapped about the outer surface of the rotating and advancing tube. Machinery for this general purpose is shown and described in Chapman Patent No. 2,812,794 and McElroy Patent No. 2,865,424.

It is also customary to provide a set of straightening rolls or elements arranged to contact the helical fin on the tube and raise the fin into position substantially normally to the axis of the tube. The fin may have its inner edge disposed in a helical slot on the tube, or soldered, or brazed to the exterior of the tube, or the fin may have the inner edge formed into a flange so that flange lies flat upon the exterior of the tube.

Use of heat exchanger tubes has demonstrated that the fin is more efficient when it has openings therethrough, such as the louvered type illustrated and described in Buschow Patent No. 2,643,863, or when it is slotted at its periphery, as shown by Rodeck Patent No. 2,372,795. A particularly effective type of fin is shown in British Patent No. 799,391, published Aug. 6, 1958.

It is an object of this invention to provide a process and apparatus for simply and rapidly forming helically finned tubing having openings therethrough, and more particularly, openings of desired shape.

Another object is to provide an apparatus and process of the character above-described in which such openings may be formed in a thin strip of metal as it is formed into a helical coil for application to the tubing.

A further object is to provide a means for so forming the fins which is adaptable for use with existing machinery with a minimum of modification.

In accordance with the present invention, the forming rolls of machinery of the general type above-described are provided with a relieved section between shoulders thereon which apply rolling stress to laterally spaced apart, longitudinally extending areas of the strip' Thus as the strip is advanced between the rolls, the longitudinal areas are differentially thinned in a direction from one edge of the strip to the other, While the intermediate area of the strip is essentially unthinned inasmuch as it is substantially unsupported. This abrupt change in longitudinal stress between the intermediate and the longitudinal areas causes the strip to part to form openings therein at spaced locations along such intermediate area.

A strip having a thickness normally used for heat exchanger fins and made of highly heat conductive material, e.g., aluminum, may part by actually tearing without prior indentation at the location of the openings to be formed. Openings formed in this manner will be generally crescent-shaped and normally spaced apart at irregular intervals. If desired, the strip may be first indented transversely of the intermediate area so as to control the spacing of the tears and, to some extent, the shape of the resulting openings. Preferably, this is accomplished by means of knives in the relieved section between shoulders on one of the rolls. Also, the strip may be preslit by extending the indentations all the way through it, thereby causing the slits to part into more uniformly shaped generally triangular openings similar to those shown in British Patent No. 799,391.

The pair of shoulders may be on the same roll or on opposite rolls, as desired, or each roll may be provided with a spaced pair of shoulders which are opposed to similar shoulders on the opposite roll. In any case, the shoulders have outer surfaces each opposed to a surface on an opposite roll. Thus, rolls cannot make metal-to-metal contact with each other in the relieved section between the shoulders.

The shape of these openings may be controlled by supporting the intermediate area of the strip in which they are to be formed, but to a substantially lesser degree than the support provided by the rolling stress applied to the longitudinal areas. Thus, the relieved section or groove between the shoulders may be substantially filled with a resilient compressible material, preferably an elastomer such as rubber or plastic materials having a selected degree of resilience, which performs the function of supporting the intermediate area of the strip to an extent preventing too great a distortion of the strip in the area between the shoulders. Since the metal of which the strip is made may be of various compositions, it is impossible to state the exact degree of resilience required, but this may be easily determined by comparing the characteristics of any particular metal which it is desired to use with those of various commercially available elastic materials. For an aluminum strip, rubber will be found to give suflicient support to the intermediate area to perform these functions.

The invention may be best understood on reference to the attached drawings wherein:

FIG. 1 is a schematic plan view of one particular machine embodying principles of the present invention;

FIG. 2 is a fragmentary perspective view of the same machine partially broken away to illustrate one operative arrangement of forming rolls;

FIG. 3 is a fragmentary detail of forming rolls showing shoulders on the driven roll defining a circumferential groove;

FIG. 4 is a fragmentary detail showing shoulders on a tapered backing roll cooperative with a cylindrical driven roll, the backing roll having a groove between the shoulders filled with a resilient compressible material;

FIG. 5 is a fragmentary detail of forming rolls having grooves between opposed shoulders on both rolls;

FIG. 6 is an end elevation of a helical fin formed from a strip indented during the stressing operation;

FIG. 7 is a detail of one preferred type of forming roll showing indenting knives in a groove between shoulders on the driven roll;

FIG. 8 is a cross-section through the forming roll of FIG. 7 on the line 8-8;

FIG. 9 ilustrates a helical fin having longitudinally spaced crescent-shaped openings therethrough formed by tearing a fiat, non-indented strip of metal;

FIG. 10 illustrates a helical fin having substantially triangular openings therein formed from a preslit strip; and

FIG. 11 illustrates another modification of forming rolls embodying features of the present invention.

In the embodiment illustrated in FIG. 1, the reference numeral 1 indicates a spool of thin, metallic strip arranged to be fed between opposed pairs of fianging rolls 2, 2a, 3 and 3a. As stated above, the use of fianging rolls is entirely optional and when a helical fin having no flange at its interior edge is desired, the fianging rolls will be omitted. In the device illustrated, guide rolls 4, 4a, and 4b guide the strip from spool 1 to the flanging rolls.

In the pair of flanging rolls 2 and 2a, a flange 11 is formed upon the upper edge of strip 8 as the strip passes between a flange 12 on roll 2 and a complementary relieved section 13 on roll 2a. It is preferred that two sets of flanging rolls be used for forming the flange, the first pair being effective to turn the flange outward at about 45 from the breadth of the strip of metal and the second pair of rolls having flanges 12a and corresponding relieved sections 13a shaped to complete the turning of the flange to a position substantially normal to the breadth of strip 8.

A guide 14 preferably is disposed to guide the strip between the opposed pair of forming rolls, which may advantageously consist of a driven roll 15 and a large tapered backing roll 16. A means 17 for simultaneously advancing and rotating a tube 18 is provided, and the forming rolls l and 16 are located upon a support 5 ad jacent to the path of axial advance of tube 18. The driven roll 15 is of substantial cylindrical shape, but has shoulders 19 and 20, best shown in FIG. 3, thereon which cooperate with the tapered backing roll 16 toreceive longitudinal areas of the strip 8 adjacent to the flange 11.

As previously mentioned, and as shown and described in Patent Nos. 2,812,794 and 2,865,424, the forming rolls are so arranged as to apply rolling stress to the opposite sides of the strip which differentially thins the strip an increasing amount in a direction from its inner to its outer edge. At least one roll of the pair may be moved in any suitable manner toward and away from the other so as to adjust the amount of thinning. Normally, the degree to which the inner and outer edges of a flat strip are thinned is proportional to the circumference of the tube relative to the outer circumference of the fin. However, in some cases, the outer edge may be over-thinned to cause it to wrinkle. In any case, this process forms the strip into a helical fin, the inner edge of which is Wrapped about the rotating tube.

Due to the fact that a machine of this general type is old in the art, the parts thereof, including the forming rolls, are shown only diagrammatically. It will be understood, however, that the faces of the opposed rolls are disposed at a small angle with respect to one another, so as to define a gradually widening space between them from the edges thereof opposite flange 11 of the strip to the edges opposite the other, free edge of the strip.

A means 21, as best shown in FIG. 2, is arranged to receive the thusly formed helical fin from the forming rolls and to guide its inner edge onto the exterior surface of the tube. The means for rotating and advancing the tube, and designated as 17, is illustrated as comprising three rotors 22, 23 and 24 arranged at the apices of a triangle and receiving the tube 18 between them to be driven by friction of the rotary members 22, 23 and 24. Since these members are not parallel to each other, but are disposed in skewed relationship, they not only rotate the tube 18 but advance it in axial direction. The rotary members 22, 23 and 24 are driven by any type of drive desired (not shown) and it is preferred that the rotation of the tube be controlled to maintain a light tension upon the helical fin as it is wound upon the tube.

Frequently, in winding a fin upon a tube in this manner, some waves or irregularities are present in the fin as it is first wound upon the tube. A straightening device, composed of members 25, 26, 27 and 28, pivoted at 29, so that they may be swung into position to receive the fin between them preferably are included in the machine. In operation, these members are moved around the pivot so that they are in position between alternate turns of the helical fin and contact with these members is sufficient to raise the fin into position substantially normal to the axis of the tube. It has been found that it is unnecessary to use silver solder or other heat conductive soldering or welding material with fins of this type when a soft aluminum fin is wound upon a brass tube or the like, since the tight fit of the flange 11 upon the exterior of tube 18 gives a heat transfer surface which is very highly effective.

It is believed that the operation of the device described is obvious from the foregoing description. In starting up, a part of the strip 8 is pulled off spool 1 and is manually threaded around the guide roll 4 where it is held in place by guide rolls 4a and 411. It is then passed between the flanging rolls 2, 2a, 3 and 3a when these are used. The strip then may be manually pulled through the guide 14 into position between roll and the roll 16, where it is gripped firmly. Power from any source (not shown) is applied to drive either roll 15, roll 16, or both. Simultaneously, the means for rotating and axially advancing tube 18 is powered and the flanged helical fin emerging from between the forming rolls 15 and 16 is guided upon the tube. The straightening members 25, 26, 27 and 28 are moved into place between consecutive turns of the fin and are lifted into position substantially normal to the axis of the tube. When the entire tube, or as much of it as is intended to be finned, has received the helical fin, the tube is removed and replaced by another and the process is repeated.

As previously described, openings 32b, shown in FIG. 9, are formed in the intermediate area of the helical fin merely by transverse tearing due to the relatively light support of such area opposite the relieved section between the shoulders 19 and 20. Although such openings are easily formed in this manner, they are sometimes irregular in spacing, as is shown in FIG. 9, and it will often be preferred to obtain more regular spacing and size of such openings in order to attain the greatest efiiciency in heat transfer between the fins and a fluid passing over them. :One preferred Way of accomplishing this result is a series of knives on one of the rolls, illustrated as knives 31 between shoulders 19a and a on roll 15a shown in FIGS. 7 and 8. Knives arranged in this manner indent the intermediate area of the strip in a transverse direction as it passes between the shoulders of the roll and the opposed roll, and thus at the same time that the rolling stress is applied to the strip. As previously described, this forms openings 32 of the type indicated in the fin 33 of FIG. 6.

Alternatively, the knives may actually penetrate through and thus preslit the strip. As a result, and as also previously described, this permits the edges of the slits to be parted into generally triangularly shaped openings 32a shown in the fin 33 of FIG. 10.

The previously described device for spacing the openings more uniformly is illustrated in FIG. 4 to comprise a cylindrical roll 15b opposed to a roll 160. The roll 160 has shoulders '34 and 35 which define a groove 36 which is substantially filled with an elastic compressible material 37, such as rubber, or other elastomer. The elastomer 37 in the groove 36 supports the intermediate area of the strip slightly, but not enough to prevent parting, and the openings formed in the strip are of more uniform character. This arrangement of rolls may be used in tearing openings in the strip, either with or without transverse indenting, or in parting slits in the strip.

The modification of the rolls shown in FIG. 5 illustrates a roll 1612 having shoulders 38 and 39 opposed to shoulders 40 and 41 on the roll 150 so that there is a groove formed in each roll.

In the modification illustrated in FIG. 11, driven roll 15d and backing roll 16d are of substantially the same diameter. Roll 15d has a shoulder 45 opposed to cylindrieal surface of roll 16d and the roll 16d has a similar shoulder 46 opposed to roll d. These shoulders provide a relieved space 47 between them. Roll 15d is mounted on a shaft 48 journaled in stationary bearings 49 and 50 carried by a support 51 and driven by any suitable drive means, illustrated as a motor 52 connected to shaft 48. Backing roll 16d is mounted on shaft 53, journaled in movable bearings 54 and 55 carried by support 51 and movable toward and away from the axis of roll 15d by screws 56 and 57. While this arrangement provides an otfset in the points of contact between the shoulders 45 and 46 and the corresponding opposite roll, the points of contact ordinarily will be out of line only by a few thousandths of an inch and a strip 58 passed between the rolls is formed into a helix, and the shape of openings formed therein may be controlled as described above without difliculty.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the process and apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. A tube finning machine, including a support, means for rotating a tube, means for moving the rotating tube and support relative to one another along the axis of the tube, rolls carried by the support and having oppositely facing shoulders for receiving a thin strip of metal therebetween, and means for driving at least one of the rolls so as to advance the strip and apply rolling stress to longitudinally extending areas of the strip opposite the shoulders for differentially thinning such longitudinally extending areas in increasing amounts in a direction from the inner to the outer edge of the strip, as the strip is so advanced, whereby said strip is formed into a helical fin to be guided about the rotating tube, said rolls having a relieved section between the shoulders so that an intermediate area of the strip between the longitudinally extending areas and opposite the relieved section is relatively unthinned, whereby said intermediate area is caused to part transversely at spaced intervals therealong.

2. The machine of claim 1, wherein the relieved section between the shoulders is substantially filled with a resilient material.

3. The machine of claim 1, wherein the pair of forming rolls consists of a small driven roll and a tapered backing roll, and the shoulders are on the driven roll.

4. The machine of claim 1, wherein the pair of forming rolls consists of a small driven roll and a tapered backing roll, and the shoulders are on the backing roll.

5. The machine of claim 1, wherein the pair of forming rolls consists of a driven roll and a tapered backing roll, both the driven roll and backing roll having spaced shoulders thereon providing a relieved section around each of the rolls between the corresponding shoulders.

6. The machine of claim 1, including means to indent the strip of metal transversely along the intermediate area thereof.

7. The machine of claim 6, wherein the means to indent comprises knives in the relieved section between the shoulders of one of the rolls.

8. A process for applying a helical fin to the exterior of a tube, which comprises the steps of applying rolling stress to the opposite sides of longitudinally extending areas of a thin strip of metal so as to advance the strip therebetween and differentially thin the strip along such longitudinally extending areas in a direction from its inner to its outer edge and thereby form it into a helical fin as it is so advanced, providing no more than relatively small support for an intermediate area of the strip between said longitudinally extending areas so that it is relatively unthinned and caused to part at a series of locations along its length as said longitudinally extending areas are thinned, and rotating the tube and simultaneously moving the tube and strip relative to one another along the axis of the tube so that the helical strip may be guided about the tube.

9. The process of claim 8, wherein the intermediate area of the strip is parted by causing it to tear.

10. The process of claim 8, including the step of lightly stressing the intermediate area of the strip.

11. The process of claim 8, including the step of providing the intermediate area of the strip with generally transversely extending indentations spaced along its length so that the strip will part at such indentations.

12. The process of claim 11, wherein the indentations are caused to penetrate the strip so as to slit it.

References Cited UNITED STATES PATENTS 2,251,642 8/1941 Tilley 113-1 2,251,074 7/1941 Sibley 29-15-73 2,583,682 1/ 1952 Celovsky.

2,635,571 4/1953 Edwards 113-1 2,661,525 12/1953 Edwards 113-1 X 2,812,794 11/1957 Chapman 29-1573 2,865,424 12/1958 McElroy 113-1 X 3,055,082 9/1962 Garland 29-1573 3,216,232 11/ 1965 Stikeleather.

FOREIGN PATENTS 989,785 4/ 1965' Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

PAUL M. COHEN, Assistant Examiner.

US. Cl. X.R. 

8. A PROCESS FOR APPLYING A HELICAL FIN TO THE EXTERIOR OF A TUBE, WHICH COMPRISES THE STEPS OF APPLYING ROLLING STRESS TO THE OPPOSITE SIDES OF LONGITUDINALLY EXTENDING AREAS OF A THIN STRIP OF METAL SO AS TO ADVANCE THE STRIP THEREBETWEEN AND DIFFERENTIALLY THIN THE STRIP ALONG SUCH LONGITUDINALLY EXTENDING AREAS IN A DIRECTION FROM ITS INNER TO ITS OUTER EDGE AND THEREBY FORM IT INTO A HELICAL FIN AS IT IS SO ADVANCED, PROVIDING NO MORE THAN RELATIVELY SMALL SUPPORT FOR AN INTERMEDIATE AREA OF THE STRIP BETWEEN SAID LONGITUDINALLY EXTENDING AREAS SO THAT IT IS RELATIVELY UNTHINNED AND CAUSED TO PART AT A SERIES OF LOCATIONS ALONG ITS LENGTH AS SAID LONGITUDINALLY EXTENDING AREAS ARE THINNED, AND ROTATING THE TUBE AND SIMULTANEOUSLY MOVING THE TUBE AND STRIP RELATIVE TO ONE ANOTHER ALOONG THE AXIS OF THE TUBE SO THAT THE HELICAL STRIP MAY BE GUIDED ABOUT THE TUBE. 